Avocado rootstock named ‘Zentmyer’

ABSTRACT

A new and distinct variety of  Persea americana  tree having a high tolerance under most conditions to  Phytophthora cinnamomi  when used as a rootstock. However, it is severely damaged by salt and is not recommended for locations where salt is a problem. This variety does not yield well under non-root rot conditions in comparison to similar varieties, making it desirable for replant situations where root rot infested soils are a problem.

Latin name of the genus and species:

The avocado cultivar of this invention is botanically identified as Persea americana Mill.

Variety denomination:

The variety denomination is ‘Zentmyer’.

BACKGROUND OF THE INVENTION

Avocado root rot is the limiting factor for the growth of avocados throughout the world. Avocado root rot is caused by the fungus Phytophthora cinnamomi, which attacks and kills the feeder roots of avocado trees. The resultant lack of roots causes the tree to eventually die from water stress. There are a number of varieties of rootstocks that have some tolerance to the disease. These varieties included ‘Duke 7’ (unpatented), the most commonly planted tolerant rootstock in the world; and ‘Thomas’ (U.S. Plant Pat. No. 6,628), another root rot tolerant rootstock. However, even with these rootstocks, growers must still use a variety of methods, including mounding, mulching and the applications of chemical fungicides, to keep the tress from dying in many soils. More resistant rootstocks are necessary to eliminate avocado root rot as a major disease threat.

Screening and Greenhouse Evaluation of Rootstocks

‘Zentmyer’ was identified and characterized using the following screening protocol. As it is difficult to breed avocados because only one in approximately one thousand flowers actually set fruit, plant breeding blocks of avocados were isolated to prevent out crossing with susceptible rootstocks. The breeding blocks were made up of various combinations of selected rootstocks including, ‘Thomas’ (U.S. Plant Pat. No. 6,628), ‘Barr Duke’ (U.S. Plant Pat. No. 6,627), ‘G6’, ‘Duke 7’, ‘Duke 9’, ‘UC 2001’, ‘UC 2011’, ‘Toro Canyon’ (U.S. Plant Pat. No. 5,642), ‘Spencer’, ‘CR1-71’, ‘G 810’, ‘G 875’, ‘G 755A’, ‘VC 256’, and ‘Steyemarkii’. In order to synchronize blooming, attempts were made to girdle late-blooming varieties and spray early-blooming varieties with the pesticide Unicona-zole-P.

Initial screening was carried out by germinating seeds, which were harvested from the breeding blocks, in flats of vermiculite in the greenhouse. Phytophthora cinnamomi-infested millet was placed in rows along with the young roots of the test seedlings. After 8-10 weeks roots were evaluated and those with a high percentage of surviving roots were transplanted to soil mix incorporated with P. cinnamomi-infested millet. Rootstocks that survived this test were planted and grown in P. cinnamomi-infested soils. Survivors were examined more carefully for various types of resistance using asexual propagated material.

-   -   a. Root survival—Rootstocks were grown in typical California         avocado soils, inoculated with P. cinnamomi and evaluated for         growth, root length and percent healthy roots.     -   b. Root regeneration—Rootstocks were grown in soil inoculated         with P. cinnamomi, treated with Aliette to halt Phytophthora         root rot and evaluated for root regeneration.     -   c. Attraction to P. cinnamomi—Roots of the rootstocks were         placed in water baths with motile zoospores of P. cinnamomi. The         numbers of spores attracted to the roots were evaluated.

Rootstocks that performed well in the screening and greenhouse evaluations were further tested under field conditions.

Selection of ‘Zentmyer’

‘Zentmyer’ was developed at Riverside, Calif. The maternal parent is ‘Thomas’ (U.S. Plant Pat. No. 6,628) avocado variety. The pollen parent is unknown. Specifically, the ‘Zentmyer’ rootstock variety was selected in 1993 from an agricultural operations land located Riverside, Calif. The fruit were collected from the avocado breeding blocks, the seed removed, and planted in vermiculite. The seeds were grown in a greenhouse. The plants were inoculated with the fungus Phytophthora cinnamomi. After showing tolerance to the disease, ‘Zentmyer’ was selected as a single plant for further testing. Budwood was collected from the plants and grafted to the stumps of adult avocado trees that had been cut down at Irvine, Calif. The new varieties grew into trees which provided budwood for further testing. At least two ‘mother’ trees of the variety are growing in Irvine Calif., along with the germplasm. During screening and evaluation, ‘Zentmyer’, which was selected and originally designated ‘PP4’, distinguished itself from other varieties, including the maternal parent ‘Thomas,’ by having a high tolerance against Phytophthora root rot. The properties of ‘Zentmyer’ were found to be true to type and transmissible by asexual reproduction.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a new and distinct avocado variety. ‘Zentmyer’ is an avocado tree having a rootstock that has a high tolerance against Phytophthora root rot under most conditions. However, it is severely damaged by salt and is not recommended for locations where salt is a problem. This variety also does not yield well under non-root rot conditions in comparison to similar varieties. For these reasons it may be an excellent choice for replant situations where root rot infested soils are a problem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a nine-year-old top-worked tree of the ‘Zentmyer’ variety while growing in Irvine, Calif.

FIG. 2 illustrates typical mature foliage of the ‘Zentmyer’ variety with dimensions in centimeters shown at the right.

FIG. 3 illustrates typical flush foliage of the ‘Zentmyer’ variety with dimensions in centimeters shown at the bottom.

FIG. 4 a illustrates typical inflorescence with dimensions in centimeters shown at the right and FIG. 4 b illustrates typical inflorescence by itself.

FIG. 5 illustrates a typical external view of the fruit of the ‘Zentmyer’ variety, with dimensions in centimeters shown at the bottom.

FIG. 6 illustrates typical internal views of the fruit of the ‘Zentmyer’ variety, with and without the seed. Dimensions in centimeters are shown at the bottom.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the new ‘Zentmyer’ variety, which was taken from an approximately nine-year-old mature tree, with the exception as a rootstock for a specific scion when reference is made to root rot resistance and salinity tolerance. The tree is located in an experimental orchard in Irvine, Calif. and is grafted on a Persea americana seedling used as a rootstock.

The Royal Horticultural Society (R.H.S.) Color Chart is used herein for the color description of the rind, seed, bark, leaf, flower, flesh color and other interest of the ‘Zentmyer’ avocado tree.

Trees, Foliage, and Flowers

-   Tree:     -   -   Growth habit.—Vigorous, upright and spreading when compared             to the rootstock ‘Thomas’.         -   Vigor.—Below are data on the vigor of ‘Hass’ grafted onto             the rootstock of ‘Zentmyer’, as determined by trunk diameter             measurements from trees planted in an orchard with             Phytophthora cinnamomi in Escondido Calif.

TABLE 1 Trunk diameter (cm) Rootstock year 1 year 2 year 3 year 4 year 5 PP#4 ‘Zentmyer’ 2.40 4.39 7.12 9.20 11.25 Thomas 2.44 4.29 6.75 8.40 10.84 Escondido Ca., with Hass scion

TABLE 2 Canopy volume (cubic feet) Rootstock year 1 year 2 year 3 year 4 year 5 PP#4 ‘Zentmyer’ 14.81 77.27 397.4 410. 1573 Thomas 13.56 84.48 388.5 367. 1076 Escondido Ca., with Hass scion

-   -   -   Size.—Medium. The typical canopy size of a three year old             top-worked ‘Thomas’ is 388 cu.ft. By comparison the canopy             size of a three year old top-worked ‘Zentmyer’ is 397 cu.ft.             The tree is 610-915 cm in height when fully grown at the             orchard site in Irvine, Calif.

-   Branch:     -   -   Color.—The color of the one year old branch is green (RHS             144D).         -   Smoothness.—The bark of a one year old branch is smooth.         -   Lenticels.—The lenticels of a one year old branch are             conspicuous.

-   Main stem:     -   -   Color.—Grayed-green (RHS 197A and RHS 197D).         -   Texture of bark.—Corky.

-   Young shoot (flush):     -   -   Intensity of anthocyanin coloration.—Weak.         -   Anthocyanin coloration.—Grayed-orange (RHS 166A).         -   Color.—Grayed-orange (RHS 166A).         -   Conspicuousness of lenticels.—Medium.         -   Color of lenticels.—Purple (RHS 185B).         -   Size of lenticels.—1.0 mm long.         -   Concentration of lenticels.—+/−26 lenticels per square cm.         -   Color of upper side.—Grayed-orange (RHS 174A).         -   Glossiness of upper side.—Medium.         -   Color of lower surface.—Grayed-orange (RHS 177A).

-   Mature leaf:     -   -   Length.—15.0 cm.         -   Width.—6.0 cm.         -   Ratio length/width.—2.5.         -   Shape.—Lanceolate.         -   Color of upper side.—Green (RHS 137A).         -   Color of lower side.—Green (RHS 138B).         -   Glossiness of upper side.—Medium.         -   Prominence of veins on lower side.—Prominent and in relief.         -   Color of veins.—Yellow-green (RHS 151A).         -   General shape and cross-section.—Concave.         -   Reflexing of apex.—Absent.         -   Color of petiole.—Yellow-green (RHS 144A).         -   Anise aroma.—Absent.         -   Margin.—Undulation of margin is absent or very weak, and the             leaf margin is entire.         -   Leaf apex shape.—Acuminate.         -   Leaf base shape.—Lanceolate.         -   Length of leaf petiole.—Approximately 3.0 cm.         -   Diameter of leaf petiole.—Approximately 3.5 mm.         -   Leaf arrangement.—Upright.

-   Flower:     -   -   Bud size.—Approximately 5 mm in length and approximately 4             mm in diameter.         -   Bud shape.—Ovoid.         -   Bud color.—Yellow-green (RHS 153A).         -   Opening.—Belongs to group “A”, male opening (i.e. with             mature stamens) occurs in the afternoon, the flower closes             over night, and female opening (i.e. with mature pistil)             occurs the next morning; the flower's opening cycle lasts             20-24 hours.         -   Petals.—Borne in two whorls of three perianth lobes. The             petals possess entire margins and petal coloration is near             yellow-green (RHS N144B). Both the upper and lower petal             surfaces are near yellow-green (RHS N144B).         -   Stamen.—There are commonly nine fertile stamens with each             having two basal nectar glands that are greyed-oranged (RHS             174A) in color and three staminodia. The anthers are             tetrathecal.         -   Pistil.—The single pistil with a slender style and small             stigmatic surface has one carpel with one ovule. The ovary             is superior.         -   Sepals.—There are 6 sepals which are approximately 7 mm in             length and approximately 4 mm in width, and the color of             both sepal surfaces is yellow-green (RHS 151A).         -   Pedicel.—Commonly approximately 7 mm in length and             approximately 1.9 mm in diameter. The coloration is near             yellow-green (RHS N144A).         -   Peduncles.—Approximately 2.0 cm in length and approximately             5.0 mm in diameter. The coloration is yellow-green (RHS             151A).         -   Number of flowers on inflorescence.—Approximately 170-200             flowers per inflorescence.         -   Fragrance.—Absent.         -   Bloom.—Bloom period at Riverside, Calif. experiment station             varies with cultural conditions. On average ‘Zentmyer’ has             been found to bloom from 1st of February through 20th of             March.             Fruit, Fruit and Production Characteristics

-   Fruit:     -   -   Length.—9.5 cm.         -   Width.—5.5 cm.         -   Ratio length/width.—1.7.         -   Weight.—146.1 grams.         -   Shape.—Obovate, with an apex and base diameter of             approximately 3.5 cm and a center diameter of approximately             5.5 cm.         -   Color of skin (when ripe).—Yellow-green (RHS 144A) with some             patches of purple (RHS N79).         -   Texture of skin.—Smooth.         -   Presence of longitudinal ridges.—Absent.         -   Thickness of skin.—Thin.         -   Adherence of skin to flesh.—Strong.         -   Main color of flesh.—Yellow-green (RHS 154C).         -   Color of intensely colored area of flesh next to skin.—Green             (RHS 140A).         -   Width of intensely colored area next to skin.—3.0 mm.         -   Conspicuousness of fibers in flesh.—Inconspicuous.

-   Seed:     -   -   Length.—5.6 cm.         -   Width.—3.4 cm.         -   Weight.—20.8 grams.         -   Shape (in longitudinal section).—Elliptical.         -   Shape (in cross section).—Circular.         -   Color of seed coat (fresh).—Grayed-orange (RHS 166B).         -   Cotyledon color.—Orange-white (RHS 159B).         -   Time of harvesting.—‘Zentmyer’ fruit ripen in September (in             Riverside Calif.).         -   Resistance to pests.—Strong resistance to Phytophthora             cinnamomi.         -   Tolerance to salinity.—Sensitive to salinity.         -   Market use.—The fruit of ‘Zentmyer’ are not intended for             market use, but rather the variety is used as a rootstock             onto which commercial varieties, such as ‘Hass’ are grafted.

TABLE 3 Rootstock rating at Santana, Ventura County, August 2001¹ Tree rating Canopy Trunk No. trees Rootstock (0-5; 5 = dead) volume (cu ft) diameter (cm) dead ‘Steddom’ 0.80 a 13.89 a 1.92 a 1 ‘Merensky II’ 0.90 a 15.10 a 1.48 a 1 ‘Uzi’ 0.90 a 16.92 a 2.02 a 0 ‘Zentmyer’ 1.05 a 16.48 a 2.05 a 1 ‘G755A 1.65 a  5.55 a 1.62 a 1 (Brokaw)’ ‘Medina’ 1.90 a 12.66 a 1.70 a 2 ‘Berg’ 2.20 a 13.80 a 1.29 a 4 ‘McKee’ 2.35 a  9.05 a 1.52 a 1 ‘Duke 7’ 2.50 a 11.40 a 1.24 a 4 ‘Thomas’ 2.65 a 10.22 a 1.15 a 4 ‘G755 A 2.75 a 11.66 a 1.49 a 2 (C&M)’ ‘UC 2023’ 3.00 a  6.21 a 1.25 a 3 ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test.

TABLE 4 Rootstock rating at Santana, Ventura County, November 2002. Two-year trial to-date. Tree rating Canopy Trunk Fruit rating (0-5; volume diameter (0-5; Rootstock 5 = dead) (cu ft) (cm) 5 = heavy) ‘Merensky 0.17 d 72.27 abc 3.49 ab 0.78 bcd II’ ‘Uzi’ 0.50 cd 69.64 abcd 3.64 a 2.50 a ‘Steddom’ 1.00 bcd 67.95 abcd 2.94 abc 1.70 abc ‘Medina’ 1.06 bcd 79.89 ab 3.26 ab 0.00 d ‘Zentmyer’ 1.50 bcd 81.44 a 3.19 ab 0.60 bcd ‘Duke 7’ 1.67 bcd 32.48 abcde 2.31 abcd 1.11 abcd ‘Berg’ 1.72 bcd 46.57 abcde 2.21 abcd 2.00 ab ‘McKee’ 1.78 abcd 30.92 bcde 2.24 abcd 0.22 cd ‘G755A 2.30 abcd 19.98 de 1.90 bcd 0.10 d (Brokaw)’ ‘Thomas’ 2.60 abc 31.50 bcde 2.02 abcd 0.30 cd ‘UC 2023’ 2.95 ab 25.50 cde 1.41 cd 0.20 d ‘G755A 4.00 a 15.71 e 0.82 d 0.00 d. (C&M)’ Tip burn Canker No. trees Rootstock rating (0-5) rating (0-5) dead ‘Merensky II’ 0.00 a 0.33 a 0/9  ‘Uzi’ 0.33 a 0.00 a 1/10 ‘Steddom’ 0.25 a 0.00 a 2/10 ‘Medina’ 0.75 a 0.00 a 1/9  ‘Zentmyer’ 0.38 a 0.63 a 1/10 ‘Duke 7’ 0.38 a 0.38 a 3/9  ‘Berg’ 0.17 a 0.83 a 3/9  ‘McKee’ 0.43 a 0.29 a 2/10 ‘G755A (Brokaw)’ 0.29 a 0.14 a 3/10 ‘Thomas’ 0.17 a 1.00 a 4/10 ‘UC 2023’ 0.00 a 0.00 a 5/10 ‘G755A (C&M)’ — — 8/10

TABLE 5 {Leo Curillo) rootstock rating, December 2003. Three-year trial to-date. Tree rating Canopy Trunk (0-5; vol diam Fruit rating Rootstocks 5 = dead) (cu ft) (cm) (0-5; 5-heavy) ‘Zentmyer’ 0.313d 48.0ab 6.45a 1.75abc ‘Merensky’ 0.556cd 71.6a 6.49a 2.67a ‘Steddom’ 0.677bcd 47.2ab 5.18ab 2.00ab ‘Parida’ 1.147abcd 50.6ab 4.91ab 1.53abcd ‘Evstro’ 1.353abcd 49.6ab 5.55ab 2.29ab ‘Merensky I’ 1.441abcd 48.6ab 5.01ab 1.41bcd ‘Guillemet’ 1.588abc 39.6b 4.58b 0.41d ‘Thomas’ 1.875ab 43.4ab 4.45b 0.72cd ‘UC 2023’ 2.188a 27.2b 4.07b 0.31d ‘VC 207’ 2.382a 32.4b 3.79b 1.12bcd Salt rating Canker No. (0-5; rating trees dead Rootstocks 5 = severe) (0-5; 5-severe) (%) ‘Zentmyer’ 0.00a 0.00a 0 ‘Merensky’ 0.00a 0.00a 0 ‘Steddom’ 0.00a 0.06a 6 ‘Parida’ 0.00a 0.07a 18 ‘Evstro’ 0.00a 0.06a 0 ‘Merensky I’ 0.00a 0.06a 18 ‘Guillemet’ 0.00a 0.08a 22 ‘Thomas’ 0.00a 0.08a 29 ‘UC 2023’ 0.08a 0.00a 19 ‘VC 207’ 0.00a 0.00a 35 Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test.

TABLE 6 Rootstock ratings of avocado trees planted in root rot soil at Escondido, July 2002 Tree Canopy Trunk Fruit set rating volume diameter rating 0-5; Rootstocks 0-5; 5 = dead Cu ft Cm 5 = heavy ‘Zentmyer’ 0.00c 397.4abc 7.12bcd 1.53cd ‘Rio Frio’ 0.00c 313.5cdef 6.33cdef 2.13bcd ‘Merens I’ 0.00c 543.6a 8.74a 3.50a ‘Merensk II’ 0.02c 409.0abc 7.81abc 2.84ab ‘VC 241’ 0.06c 238.4defg 6.19defg 1.41cd ‘Uzi’ 0.29bc 504.3ab 8.57ab 2.76ab ‘Steddom’ 0.36bc 376.1bcde 7.07bcd 2.43bc ‘Thomas’ 0.44bc 388.5bcd 6.75cde 1.12de ‘Guillemet’ 0.59bc 192.0fgh 4.90fgh 1.12de ‘Spencer sdlg’ 0.63bc 225.8efg 5.24efgh 1.56cd ‘Leo’ 0.67bc 288.2cdef 5.89defgh 1.60cd ‘Spencer clonal’ 0.69bc 163.8fgh 4.65gh 1.54cd ‘Duke 7’ 1.00b 129.3gh 4.38h 1.47cd ‘G755A’ 0.16b 294.1cdef 5.86defgh 1.56cd ‘PolyN’ 4.12a 65.6h 1.26i 0.24e Tip Burn Cankers Dead Rootstocks Number trees affected ‘Zentmyer’ 0 0 0/15 ‘Rio Frio’ 0 0 0/16 ‘Merens I’ 0 0 0/14 ‘Merensk II’ 0 1 0/17 ‘VC 241’ 0 0 0/16 ‘Uzi’ 2 0 1/17 ‘Steddom’ 0 0 1/14 ‘Thomas’ 0 0 1/17 ‘Guillemet’ 3 1 2/17 ‘Spencer sdlg’ 0 0 2/16 ‘Leo’ 0 0 2/15 ‘Spencer clonal’ 0 0 5/16 ‘Duke 7’ 0 0 3/15 ‘G755A’ 2 1 3/16 ‘PolyN’ 0 0 14/17 

TABLE 7 rootstock trial tree ratio April 2003¹. Four-year trial to-date Tree rating Canopy Trunk Rootstock (0-5; 5 = dead) volume (cu ft) diam. (cm) Salt ‘MerenI’ 0.00d 551ab  10.7a 0.08cd ‘VC241’ 0.06d 281efgh 8.0abc 0.03cd ‘Rio Frio’ 0.07d 362efcd 8.7abc 0.00d ‘Zentmyer’ 0.07d  410bcde 9.2ab 0.32bc ‘MerenII’ 0.18d 532abc  9.4ab 0.21dc ‘Spen sdlg’ 0.36d 263efgh 6.9bc 0.00d ‘Uzi’ 0.38d 669a   10.6a 0.68a ‘Steddom’ 0.39d 478bcd  8.6abc 0.32bc ‘Thomas’ 0.47cd 367cdef 8.4abc 0.62ab ‘Leo’ 0.77cbd 274efgh 7.3abc 0.13cd ‘Guillemet’ 0.83cbd 190ghi  6.2bc 0.13cd ‘Duke7’ 1.34cb 127hi  8.8abc 0.16cd ‘Spen cl’ 1.44b 211fghi  5.3c 0.12cd ‘G755A’ 1.69b 322defg 7.0bc 0.25cd ‘PolyN’ 4.15a 77i   1.5d 0.06cd Canker Fruit Dead trees Rootstock (0-5; 5 = heavy) rating² (%) ‘MerenI’ 0a 2.97abc 0 ‘VC241’ 0a 3.41ab 0 ‘Rio Frio’ 0a 3.73a 0 ‘Zentmyer’ 0a 3.71a 0 ‘MerenII’   0.1a 2.97abc 0 ‘Spen sdlg’ 0a 3.57ab 7 ‘Uzi’ 0a 3.47ab 6 ‘Steddom’ 0a 3.75a 7 ‘Thomas’ 0a 3.53ab 6 ‘Leo’ 0a 3.29ab 13 ‘Guillemet’ 0a 2.90abc 13 ‘Duke7’ 0a 1.53de 19 ‘Spen cl’ 0a 2.35bcd 23 ‘G755A’ 0a 1.78cd 25 ‘PolyN’ 0a 0.29e 82 ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test. ²Fruit was rated in November 2003.

TABLE 8 Temecula, yield 2003^(1;2). Four year trial to-date. Fruit weight/tree Number Fruit weight Rootstock (kg) fruit/tree (kg) ‘Zentmyer’ 15.89a 68.64a 0.219a ‘Uzi’ 13.99ab 59.24ab 0.195ab ‘Spencer 12.52ab 56.27ab 0.181ab seedling’ ‘Merensky II’ 11.83ab 51.12ab 0.185ab ‘Rio Frio’ 10.87abc 51.33ab 0.187ab ‘Steddom’ 10.01abc 46.20abc 0.175abc ‘Thomas’ 8.50abcd 40.12abcd 0.154abc ‘G755A’ 8.08abcd 34.56abcd 0.116bc ‘VC241’ 7.44bcd 31.75bcd 0.202ab ‘Guillemet’ 7.42bcd 30.00bcd 0.196ab ‘Spencer clonal’ 6.99bcd 32.00bcd 0.136abc ‘Merensky I’ 6.95bcd 32.08bcd 0.148abc ‘Leo’ 6.53bcd 28.14bcd 0.140abc ‘Duke 7’ 3.33cd 14.81cd 0.138abc ‘PolyN’ 1.72d 5.71d 0.076c ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test. ²Only fruit which were grade size were picked; remaining fruit on trees to be picked later.

TABLE 9 Escondido, Tree ratings, July 2002 Tree rating Canopy Trunk diam Rootstock (0-5; 5 = dead) vol. (cu ft) (cm) ‘Uzi’ 0.039 b 34.69 a 2.43 a ‘Guillemet’ 0.042 b 22.86 a 2.06 a ‘Zentmyer’ 0.077 b 22.40 a 2.25 a ‘Spencer sdlg’ 0.536 b 27.81 a 2.01 a ‘Steddom’ 0.615 b 18.93 a 1.99 a ‘Berg’ 0.714 b 21.42 a 1.98 a ‘Merensky II’ 0.750 b 32.07 a 2.10 a ‘Elinor’ 0.786 b 29.44 a 2.03 a ‘Thomas’ 0.846 b 23.07 a 1.85 a ‘Pond’ 1.00 ab 30.55 a 2.15 a ‘Crowley’ 1.083 ab 23.78 a 1.86 a ‘G755A’ 1.231 ab 22.64 a 1.85 a ‘Duke 9’ 2.270 a 9.40 a 1.07 b No. trees No. trees No. trees Rootstock Dead w/ tip burn w/ canker ‘Uzi’ 0 6 0 ‘Guillemet’ 0 4 0 ‘Zentmyer’ 0 2 0 ‘Spencer sdlg’ 0 2 1 ‘Steddom’ 1 0 0 ‘Berg’ 0 1 2 ‘Merensky II’ 2 0 1 ‘Elinor’ 1 0 2 ‘Thomas’ 1 2 0 ‘Pond’ 1 0 2 ‘Crowley’ 2 1 0 ‘G755A’ 2 0 0 ‘Duke 9’ 5 0 0 There were significant differences at P = 0.01 between blocks for all tree parameters analyzed.

TABLE 10 Tree ratings, April 2003. Two-year trial to-date. Tree rating Canopy Trunk Fruit rating (0-5; vol diam (0-5; Rootstock 5 = dead) (cu ft) (cm) 5 = heavy) ‘Uzi’ 0.267 c 88.76 a 4.193 a 0.0 a ‘Berg’ 0.531 c 44.16 a 2.956 bc 0.0 a ‘Zentmyer’ 0.600 c 54.37 a 3.393 ab 0.0 a ‘Merensky 0.833 bc 68.49 a 3.333 ab 0.0 a II’ ‘Steddom’ 0.867 bc 56.42 a 3.127 ab 0.0 a ‘Pond’ 0.906 bc 55.05 a 3.188 ab 0.0 a ‘Spenser 0.906 bc 51.45 a 2.988 bc 0.0 a sdlg’ ‘Crowley’ 0.964 bc 42.05 a 3.021 bc 0.0 a ‘Thomas’ 1.071 bc 49.99 a 2.900 bc 0.0 a ‘Guillemet’ 0.167 abc 43.64 a 2.960 bc 0.1 a ‘Elinor’ 1.393 abc 58.40 a 2.864 bc 0.0 a ‘G755A’ 2.156 ab 44.21 a 2.819 bc 0.0 a ‘Duke 9’ 2.577 a 32.16 a 1.885 c 0.0 a Salt rating Canker rating No. trees Rootstock (0-5; 5 = severe) (0-5; 5 = severe) Dead (%) ‘Uzi’ 0.933 ab 0.000 a 0 ‘Berg’ 0.633 abcd 0.000 a 6 ‘Zentmyer’ 1.000 a 0.000 a 7 ‘Merensky II’ 0.154 cd 0.308 a 13 ‘Steddom’ 0.321 bcd 0.286 a 7 ‘Pond’ 0.767 abc 0.200 a 6 ‘Spenser sdlg’ 0.300 bcd 0.200 a 6 ‘Crowley’ 0.083 d 0.000 a 14 ‘Thomas’ 0.731 abc 0.000 a 0 ‘Guillemet’ 0.615 abcd 0.133 a 13 ‘Elinor’ 0.333 bcd 0.167 a 14 ‘G755A’ 0.846 ab 0.077 a 13 ‘Duke 9’ 0.313 bcd 0.500 a 38

TABLE 11 Santa Paula, rootstock rating, December 2002 Tree rating Canopy Trunk Rootstock (0-5; 5 = dead) vol (cu ft) diam (cm) Fruit set ‘McKee’ 0.00 b 51.41 a 3.45 bc 0.00 a ‘Merensky II’ 0.00 b 53.45 a 3.66 ab 0.00 a ‘Pond’ 0.00 b 55.08 a 3.69 a 0.00 a ‘Guillemet’ 0.00 b 37.98 b 2.71 f 0.00 a ‘Zentmyer’ 0.00 b 51.92 a 3.38 cd 0.00 a ‘Thomas’ 0.00 b 36.66 b 3.15 de 0.00 a ‘Crowley’ 0.03 b 34.91 b 3.17 d 0.05 a ‘Duke 9’ 0.05 b 31.93 b 2.93 ef 0.00 a ‘Steddom’ 0.27 a 37.14 b 2.75 f 0.00 a Salt burn Trees Rootstock (0-5; 5-heavy) Cankers dead (%) ‘McKee’ 0 0 0 ‘Merensky II’ 0 0 0 ‘Pond’ 0 0 0 ‘Guillemet’ 0 0 0 ‘Zentmyer’ 0 0 0 ‘Thomas’ 0 0 0 ‘Crowley’ 0 0 0 ‘Duke 9’ 0 0 0 ‘Steddom’ 0 0 0 Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio.

TABLE 12 Santa Paula, rootstock rating, December 2003. Two-year trial to-date. Tree rating Canopy Trunk Fruit Rootstock (0-5; 5 = dead) vol (cu ft) diam (cm) set ‘McKee’ 0.025b 184.1b 5.88bc 1.90ab ‘Merensky II’ 0.000b 246.8a 6.18abc 2.60a ‘Pond’ 0.000b 192.0b 6.24ab 0.00d ‘Guillemet’ 0.000b 118.8cd 5.38de 0.00d ‘Zentmyer’ 0.026b 182.8b 6.41a 1.32bc ‘Thomas’ 0.237a 174.9b 5.72cd 0.47cd ‘Crowley’ 0.150ab 124.7c 5.42de 2.15ab ‘Duke 9’ 0.053ab 132.6c 5.19e 1.89ab ‘Steddom’ 0.083ab 86.3d 5.00e 2.00ab Salt burn Trees Rootstock (0-5; 5-heavy) Cankers dead (%) ‘McKee’ 0 0 0 ‘Merensky II’ 0 0 0 ‘Pond’ 0 0 0 ‘Guillemet’ 0 0 0 ‘Zentmyer’ 0 0 0 ‘Thomas’ 0 0 0 ‘Crowley’ 0 0 0 ‘Duke 9’ 0 0 0 ‘Steddom’ 0 0 0 Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test..

TABLE 13 Temecula rootstock ratings, Sept 2002 Tree rating Fruit rating (0-5; Canopy Trunk (0-5; Rootstock 5 = dead) vol (cu ft) diam (cm) 5 = heavy) ‘Zentmyer’ 0.400 c 40.70 ab 2.79 a 0.00 b ‘Crowley’ 0.618 c 40.38 ab 2.86 a 0.00 b ‘Elinor’ 0.824 c 40.52 ab 2.54 a 0.00 b ‘Guillemet’ 0.882 bc 39.13 ab 2.42 a 0.00 b ‘Steddom’ 0.969 bc 29.20 bc 2.13 ab 1.16 a ‘Thomas’ 0.969 bc 31.46 bc 2.13 ab 0.00 b ‘Pond’ 1.088 bc 54.08 a 2.78 a 0.00 b ‘Uzi’ 1.188 bc 35.08 ab 2.56 a 0.00 b ‘G755A’ 2.088 ab 37.85 ab 2.41 a 0.00 b ‘Spencer 2.906 a 11.96 c 1.39 b 0.00 b sdlg’ No. Salt damage Cankers trees Rootstock (0-5; 5 = heavy) (0-5; 5 = heavy) dead ‘Zentmyer’ 1.50 ab 0.00 a 0/15 ‘Crowley’ 1.34 b 0.00 a 1/17 ‘Elinor’ 1.59 ab 0.00 a 1/17 ‘Guillemet’ 1.41 b 0.00 a 2/17 ‘Steddom’ 1.54 ab 0.50 a 2/16 ‘Thomas’ 1.50 ab 0.00 a 3/16 ‘Pond’ 1.40 b 0.00 a 2/17 ‘Uzi’ 1.64 ab 0.00 a 2/16 ‘G755A’ 2.50 ab 0.36 a 4/17 ‘Spencer sdlg’ 2.63 a 0.00 a 4/16

TABLE 14 Temecula, rootstock ratings, December 2003. Two-year trial to-date. Tree rating Fruit rating (0-5; Canopy Trunk (0-5; Rootstock 5 = dead) vol (cu ft) diam (cm) 5 = heavy) ‘Zentmyer’ 0.313c 207.27a 6.23a 2.063a ‘Pond’ 0.906c 307.04a 5.75a 1.813a ‘Elinor’ 0.912c 170.37a 4.80a. 1.059a ‘Guillemet’ 1.059c 199.37a 5.73a 0.882a ‘Uzi’ 1.094bc 206.04a 4.35a 0.813a ‘Crowley’ 1.250bc 144.14a 5.04a 1.438a ‘Steddom’ 1.281bc 254.94a 4.89a 1.188a ‘Thomas’ 1.313be 226.39a 5.16a 1.375a ‘G755A’ 2.438ab 175.55a 5.23a 0.625a ‘Spencer 2.813a 42.12a 2.26a 0.519a sdlg’ Salt damage Cankers Trees Rootstock (0-5; 5 = heavy) (0-5; 5 = heavy) dead (%) ‘Zentmyer’ 1.188ab 0.000a 0 ‘Pond’ 0.321cd 0.000a 13 ‘Elinor’ 0.469cd 0.000a 6 ‘Guillemet’ 0.893abc 0.000a 18 ‘Uzi’ 0.769abcd 0.000a 19 ‘Crowley’ 0.731abcd 0.000a 19 ‘Steddom’ 0.167d 0.000a 25 ‘Thomas’ 1.308a 0.000a 19 ‘G755A’ 1.167ab 0.000a 25 ‘Spencer sdlg’ 0.500bcd 0.000a 44 

What is claimed is:
 1. A new and distinct rootstock variety of avocado tree having the characteristics substantially as described and illustrated herein. 